The regenerative halogenation process is accomplished by contacting a polymer, which has been dissolved in a solvent, a halogenating agent, and an emulsion. The halogenating agent includes but is not limited to molecular bromine, bromine chloride, hydrogen bromide, sodium bromide, or a mixture thereof. The emulsion is a mixture of a water soluble oxidizing agent capable of converting hydrogen halide to a free halogen, an emulsifying agent, an organic solvent, and water. The halogenated polymer is recovered from the mixture. More information about known regenerative halogenation processes is disclosed in U.S. Pat. Nos. 5,681,901 and 5,569,723.
While halogenated polymers manufactured using the regenerative process yield a greater maximum theoretical halogenation utilization compared to conventional halogenation methods, the regenerative process results in increased levels of Mooney viscosity growth of the polymers when compared with polymers halogenated by the conventional methods. Mooney viscosity growth, or Mooney growth, can lead to unsatisfactory processability of compound formulations, such as innerliner formulations. Unlike bromobutyl polymers, chlorobutyl polymers generally do not experience the same degree of increasing Mooney viscosity as bromobutyl polymers due to the greater bonding strength of chlorine and the associated backbone carbon, as compared to bromine, to the polymer structure. FIG. 3 shows the change in Mooney viscosity for both conventionally produced bromobutyl and prior bromine regenerative produced bromobutyl. As seen in FIG. 3, all bromobutyl polymers undergo some degree of increase in the Mooney viscosity as the polymer ages. For bromine regenerative produced bromobutyl, the slope of the increase in Mooney viscosity is greater. For instance, Mooney viscosity growth of polymers prepared by regeneration is about twice that of polymers prepared by conventional methods stored in warehouse conditions for about 2.5 years (approximated by an Oven Aging Test described later herein). While a small increase in polymer Mooney viscosity does not negatively alter the products made using the polymer, or alter any manufacturing processes using the polymer, accelerated Mooney viscosity growth reduces the shelf life of the halogenated polymer.
U.S. Ser. No. 61/946,018, filed on Feb. 28, 2014, discloses adding free radical scavengers to the final polymers produced by the conventional and bromine regeneration processes to suppress the Mooney viscosity growth. U.S. Ser. No. 61/946,035, filed on Feb. 28, 2014, discloses adding an ionomer stabilizer to the final elastomeric nanocomposite to suppress the Mooney growth. There is still a need to modify the regenerative halogenation process known in the art whereby the resulting polymer has a reduced Mooney viscosity growth.